Hello everyone!
I'm Guna, new to this forum. I need clarification regard to need for a selaer for rebuilt copper part with same material. The part will be immersed in a solution and used as cathode. Since the materials are of same kind I think it is not necessary for a sealer. Am I correct?

(03-22-2010 01:55 AM)Guna Wrote: Hello everyone!
I'm Guna, new to this forum. I need clarification regard to need for a selaer for rebuilt copper part with same material. The part will be immersed in a solution and used as cathode. Since the materials are of same kind I think it is not necessary for a sealer. Am I correct?

Thank you
Guna

I would seriously consider using a sealer to prevent corrosion from penetrating your coating and delaminating it from the substrate metal. A coating will fail very quickly if it loses its base. I don't think using the sealer will hurt your repair, so just for good measure, I would use it.

Matching closely as possible coating with substrate, will certainly minimise potential for galvanic corrosion. But, there are differences between coating and substrate physically and chemically (I am assuming your coating is thermally sprayed). The copper coating will probably contain copper oxides. While copper may be resistant to the solution, copper oxides may not.

I would be inclined to test both sealed and unsealed coatings and see which performs best for your application.

Matching closely as possible coating with substrate, will certainly minimise potential for galvanic corrosion. But, there are differences between coating and substrate physically and chemically (I am assuming your coating is thermally sprayed). The copper coating will probably contain copper oxides. While copper may be resistant to the solution, copper oxides may not.

I would be inclined to test both sealed and unsealed coatings and see which performs best for your application.

Dear All,
Thank you for the advises especially by Gordon which explained the differance between coating and substrate.

(03-22-2010 01:55 AM)Guna Wrote: Hello everyone!
I'm Guna, new to this forum. I need clarification regard to need for a selaer for rebuilt copper part with same material. The part will be immersed in a solution and used as cathode. Since the materials are of same kind I think it is not necessary for a sealer. Am I correct?

Thank you
Guna

Hi

i don't understand why there should be galvanic corrosion; if i 've understood well the is just one metal, copper.
Also to assess likelihood of galvanic corrosion other factors like the type of electrolyte and area ratio of the two metal should be considered.

Hi, I agree with Gordon about corrosion, but I think the mother problem will be the adhesion, because using copper as base material, is very difficoult to coat, it has a very poor bond with every kind of materials, particularly using copper as bond/top coat, maybe using HVOF wire will be a little better..

The fact that the sprayed copper is being used as a cathode means that a sealer may be inherently detrimental to its operation in this condition. The sealer reduces the surface area of the copper in contact with the electrolyte and therefore reduces its ability to act as a cathode.

A big question for you is the anticipated service life of the system in question. In a VERY similar application I have used and Aluminum Bronze bond coat with pure copper applied over the top of it because the bond characteristics of the Al make for a much better coating and the galvanic action between the two is negligible for the service life of the parts (which is fairly short in this case).

No matter which spray process you use, there will always be some porosity. The corrosive liquid will penetrate the coating and attack the copper. The overall surface area will be large, so the coating should be degraded faster than cast copper. For this reason, I would certainly choose to err on the safe side and apply a sealer. There will still be plenty of copper to carry electrical current.